Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $95.53   9.215%   $104.3331   $104.33   $104.35   $104.30  
  Purchase #2 $56.66   8.862%   $61.6812   $61.68   $61.70   $61.70  
  Purchase #3 $22.61   8.378%   $24.5043   $24.50   $24.50   $24.50  
  Purchase #4 $201.56   12.432%   $226.6179   $226.62   $226.60   $226.60  
  Purchase #5 $220.60   6.767%   $235.528   $235.53   $235.55   $235.50  
  Purchase #6 $81.67   11.126%   $90.7566   $90.76   $90.75   $90.80  
  Purchase #7 $220.77   6.259%   $234.588   $234.59   $234.60   $234.60  
  7 purchase totals = $899.40       $978.0091   $978.01   $978.05   $978.00